C.S. Ratheesh Kumar

Biogeochemistry of surficial sediments in the intertidal systems of a tropical environment

Variability of nature and composition of organic matter in the surficial sediments of mangrove and estuarine systems of Cochin were investigated. Assessment of biochemical composition and elements such as carbon, nitrogen and sulphur were employed for this. Irrespective of the higher content of total organic matter, the labile organic matter was very low in both mangrove and estuarine sediments. Concentrations of biochemical compounds were comparatively higher in mangrove sediments. Total lipids were the dominant class among labile organic compounds in both mangrove and estuarine sediments contributing 51.4% and 45.3%, respectively. Protein to carbohydrate ratio was higher in estuarine sediments when compared to mangroves, indicating low dead organic matter accumulation, probably due to the strong hydrodynamic conditions in estuaries. Correlation analysis showed that sediment texture had no significant correlation with any of the sedimentary parameters in mangroves, whereas in estuaries, it showed significant correlations with most of the sedimentary parameters. Principal component analysis indicated three different dominant processes in mangroves namely mangrove litter addition, diagenesis and other geochemical process like siltation and sorption/desorption, while in estuaries the dominant process seems to be diagenesis.

Biogeochemical facsimile of the organic matter quality and trophic status of a micro-tidal tropical estuary

Seasonal studies were carried out from 21 stations, comprising of three zones, of Cochin Estuary, to assess the organic matter quality and trophic status. The hydographical parameters showed significant seasonal variations and nutrients and chlorophylls were generally higher during the monsoon season. However, chemical contamination along with the seasonal limitations of light and nitrogen imposed restrictions on the primary production and as a result, mesotrophic conditions generally prevailed in the water column. The nutrient stoichometries and δ13C values of surficial sediments indicated significant allochthonous contribution of organic matter. Irrespective of the higher content of total organic matter, the labile organic matter was very low. Dominance of carbohydrates over lipids and proteins indicated the lower nutritive aspect of the organic matter, and their aged and refractory nature. This, along with higher amount of phytodetritus and the low algal contribution to the biopolymeric carbon corroborated the dominance of allochthonous organic matter and the heterotrophic nature. The spatial and seasonal variations of labile organic components could effectively substantiate the observed shift in the productivity pattern. An alternative ratio, lipids to tannins and lignins, was proposed to ascertain the relative contribution of allochthonous organic matter in the estuary. This study confirmed the efficiency of an integrated biogeochemical approach to establish zones with distinct benthic trophic status associated with different degrees of natural and anthropogenic input. Nevertheless, our results also suggest that the biochemical composition alone could lead to erroneous conclusions in the case of regions that receive enormous amounts of anthropogenic inputs.

Assessment of Organic Matter Sources in the Tropical Mangrove Ecosystems of Cochin, Southwest India

The sources of organic matter in three typical mangrove systems of Cochin estuary were assessed for the first time with help of sediment bulk parameters and fatty acid biomarkers. The C/N and δ13C analysis showed intermediate values to that of autochthonous and terrestrial inputs of organic matter, signaling to a mixed origin. The biochemical composition of sedimentary organic matter revealed a dominance of lipids over proteins and carbohydrates, indicating the nutritive or energetic value as well as the freshness of organic matter in all the systems. Fatty acids ranging from C8 to C24 were identified in the study. C20:5n-3 was one of the major fatty acids at station 1, indicating significant benthic phytoplankton contribution. The zooplankton biomarkers C20:1 and C24:1 were also present in appreciable levels, suggesting the tidal influx. Principal fatty acids at station 2 were the zooplankton biomarkers C20:1 and C24:1 implying significant estuarine contribution through tidal influx. The major fatty acids at station 3 were diatom marker C20:5n-3 and the higher plant marker C24:0. Dominant fatty acids in mangrove leaves; C18:2n-6 and C18:3n-3 were also present at station 3. The low contributions of C20:1 and C24:1 confirms the limited tidal exchange at this station. Presence of significant amount polyunsaturated fatty acids in the mangrove sediments confirms the freshness of organic matter. Thus, fatty acid biomarker study of the three mangrove systems of Cochin estuary could substantiate the bulk parameter approaches effectively; distinguishing the multiple sources of the organic matter and the observed spatial variations.

Aliphatic and polycyclic aromatic hydrocarbon contamination in surface sediment of the Chitrapuzha River, South West India

ABSTRACT Distribution (seasonal and spatial) of aliphatic and polycyclic aromatic hydrocarbons (PAHs) in surface sediments of the Chitrapuzha River, Cochin, India, was investigated using gas chromatography. Significantly high concentrations prevailed during the pre-monsoon season with the industrial zones of the river appearing to be hot spots with particularly elevated levels of the hydrocarbons. AHCs ranged between 7754 and 41,173 ng/g with an average of 25,256 ng/g, while total PAHs varied from 5046 to 33,087 ng/g. n-Alkane indices and PAH diagnostic ratios point to petroleum contamination in the sediments. The significance of PAHs in the sediments was explored using universally accepted interpretation tools. Observed levels of PAHs in sediments of Chitrapuzha are likely to cause adverse effects on biota.

Heavy metal distribution and contamination status in the sedimentary environment of Cochin estuary

Heavy metals (Fe, Mn, Cr, Zn, Ni, Pb, Cu, Co and Cd) in the surface sediments of Cochin estuary, Southwest coast of India were analyzed to understand the spatio-temporal variation and contamination status via six sampling campaigns. Pollution indices like enrichment factor, geoaccumulation index and pollution load index inferred that the sediments of the northern arm of the estuary exhibited severe trace metal accumulation. Numerical sediment quality guidelines were applied to assess adverse biological effects of the trace metals, suggesting that occasional biological effect may occur due to Cr, Cu, Ni and Pb. Correlations between metals, organic carbon, silt and clay suggested that both fine grained sediment and organic matter were important carriers for these metals. Multivariate statistics indicated that the sources of Cu and Ni resulted primarily from natural weathering processes, whereas enriched levels of Cd, Cr, Zn and Pb were mainly attributed to anthropogenic activities.

Fate and source distribution of organic constituents in a river-dominated tropical estuary

We investigated spatial and temporal changes in the quality of sedimentary organic matter and trophic status of the Cochin estuarine system, southwest coast of India. Sediment samples were collected in five sampling campaigns from January 2009 to April 2010. TOC/N ratio implied mixed input of autochthonous as well as remarkable allochthonous terrestrial higher plant debris into the sedimentary system. More depleted δ13C values at riverine and industrial zone suggested a major contribution of terrestrial higher plant debris to sedimentary organic matter. Trophic status of the estuary changed seasonally to eutrophic via oligotrophic and mesotrophic conditions during the period January 2009 to April 2010. The protein to carbohydrate ratio was lower (<1), indicating heterotrophic nature and the higher lipid to carbohydrate ratio (>1) denoted preservation of lipid compounds in the sediments. Correlation analyses provide evidence of the association of chlorophyll pigments with carbohydrates and account for the highly productive nature of the estuary and algal contributions to organic matter. Canonical correspondence analysis clearly illustrated prominence of phaeopigments in fishing zone, lipids in sewage/tourism influenced zone, carbohydrates in riverine zone and proteins in industrial zone. It also indicated the influence of sedimentary texture, pH and organic carbon to the distribution of biochemical constituents.

Amino acids as indicators to elucidate organic matter degradation profile in the Cochin estuarine sediments, Southwest coast of India

Surface sediments from three zones (fresh water, estuarine, and riverine/industrial zones) of the Cochin estuary, Southwest coast of India, were seasonally analyzed to understand the nature and degradation status of organic matter. Amino acid-based indices such as total hydrolyzable amino acids (THAAs), percentage contributions of amino acid carbon to total organic carbon (THAA-C%) and those of amino acid nitrogen to total nitrogen (THAA-N%), and degradation index (DI) were calculated. Elevated levels of amino acids in the sediments of the estuary were attributed to river runoff, autochthonous production, allochthonous inputs, and industrial and domestic effluent discharges. Higher levels of THAA-C%, THAA-N%, THAA, and positive DI found in most of the stations suggest the fresh deposition of organic matter. Multivariate statistical analyses revealed that the dispersal pattern of amino acids depends on the sediment texture, organic matter, redox state, and microbial processes in the study region.

Geochemical distribution, bioavailability and potential toxicity of some trace metals in a complex micro-tidal estuary, Southwest India

The spatial and temporal variations of some trace metals in the surface sediments of Cochin Estuary were analyzed along with their geochemical associations to identify the possible sources, bioavailability and the health risks posed by them. The dominance of kaolinite and suggested that clay minerals distribution is influenced by sediment sorting. Total metal analysis revealed enrichment for Cd, Pb and Zn due to anthropogenic activities. The speciation analysis established that notwithstanding the large availability, carbonate as well as organic and sulfides bound fractions showed negligible associations with most of the metals. Hydrous Fe–Mn oxides appeared to play a major role in controlling the fate and transport of these metals in the sediments of Cochin Estuary. Lower contribution of the residual fractions for Cd (21%–26%), Pb (<60%) and Zn (24%–42%) indicated an obvious increase of other geochemical fractions. Risk assessment analysis revealed that regardless of total concentration, none of the analyzed metals were at safe levels in the estuary as appreciable percentages were found to be associated with mobile geochemical forms. The speciation study conspicuously established that the metals originating from non-geogenic sources are largely associated with the labile fractions and hence are more detrimental to the aquatic biota.